Move Pool and Poolable out of com.amazon.ion.impl.bin.utf8 package #406
Description
These classes have nothing to do with UTF-8. They are base classes for object pools that happen to be used by the UTF-8 encoder/decoder pools.
They should probably be moved up to com.amazon.ion.impl, although this would require making them public unless we move all pools to com.amazon.ion.impl, or move all pool-related things to a different package like com.amazon.ion.impl.pool.